Recently developed, the Cloud Infrared Radiometer CIR-7, operates 7 infrared sensors, each with a 6-degree field of view, and spectral range 8-14 μm. The sensors are mounted on a semi-circular band at angles 0, 12, 24, 36, 48, 60 and 72°. A "hemispherical" mosaic of 181 brightness temperature measurements centered on the zenith is obtained by the rotation of the band around the vertical axis, performing 30 scans, every 12° from 0° (North) to 348 °. We present an algorithm that utilizes the brightness temperatures from the CIR-7 given the precipitable water vapor amounts and vertical profiles of the thermodynamic state of the atmosphere from independent measurements. It estimates the total cloud amount, the amount of low, middle and high clouds, maps out the spatial distribution of the cloud field and determines the vertical distribution of the clouds by computing cloud base heights. The algorithm is validated through comparisons with well studied ground-based and satellite retrieval techniques. Initial analyses show good cloud amount assessment and spatial mapping abilities. The estimated mean absolute cloud amount difference for day time is 12.3% when compared to the amount of opaque clouds derived with a total sky imager (TSI). For night time, this difference is 19.4% comparing to the effective cloud fraction derived with an atmospheric emitted radiance interferometer (AERI). The vertical distribution understanding is currently limited; however, the amounts of low, middle and high clouds could be determined and studied further.

In this work a method for determining the micro- and macro-physical properties of oceanic stratocumulus clouds at night-time (when only infrared data are available) is presented. It is based on the inversion of a radiative transfer model that computes the brightness temperatures in NOAA-AVHRR channels 3, 4 and 5. The inversion is performed using an artificial neural network (ANN), which is trained to fit the theoretical computations. A detailed study of the ANN parameters and training algorithms demonstrates the convenience of using the "back propagation with momentum" method. The proposed retrieval, using both uniform and adiabatic models for clouds, was validated using ground data collected in Tenerife (Canary Islands), and a good agreement was obtained in those pixels near the sample site. The convenience of using the adiabatic approximation is discussed.

It is of great interest to investigate the radiative properties on the cloud optical, microphysical, and geometrical properties of clouds that play crucial role in the climate system. Here, top height, base height, and geometrical thickness of cloud layer are considered as cloud geometrical properties. Several studies show that information of some spectral regions including oxygen A-band, enables us to retrieve the cloud geometrical properties as well as the optical thickness, the effective particle radius of cloud. In this study, an algorithm was developed to retrieve simultaneously the cloud optical thickness, effective particle radius, top height, and geometrical thickness of cloud layer with the spectral information of visible, near infrared, thermal infrared, and oxygen A-band channels. This algorithm was applied to ADEOS-II / GLI dataset so as to retrieve global distribution of cloud geometrical properties. The retrieved results around Japan are not strange and to be validated with other observation in the near future. This study will expand to the global analysis and be anticipated to contribute to the earth climate studies in terms of cloud optical, microphysical, and geometrical properties.

Current uncertainties in the role of aerosols and clouds in the Earth's climate system limit our abilities to model the climate system and predict climate change. These limitations are due primarily to difficulties of adequately measuring aerosols and clouds on a global scale. The A-train satellites (Aqua, CALIPSO, CloudSat, PARASOL, and Aura) will provide an unprecedented opportunity to address these uncertainties. The various active and passive sensors of the A-train will use a variety of measurement techniques to provide comprehensive observations of the multi-dimensional properties of clouds and aerosols. However, to fully achieve the potential of this ensemble requires a robust data analysis framework to optimally and efficiently map these individual measurements into a comprehensive set of cloud and aerosol physical properties. In this work we introduce the Multi-Instrument Data Analysis and Synthesis (MIDAS) project, whose goal is to develop a suite of physically sound and computationally efficient algorithms that will combine active and passive remote sensing data in order to produce improved assessments of aerosol and cloud radiative and microphysical properties. These algorithms include (a) the development of an intelligent feature detection algorithm that combines inputs from both active and passive sensors, and (b) identifying recognizable multi-instrument signatures related to aerosol and cloud type derived from clusters of image pixels and the associated vertical profile information. Classification of these signatures will lead to the automated identification of aerosol and cloud types. Testing of these new algorithms is done using currently existing and readily available active and passive measurements from the Cloud Physics Lidar and the MODIS Airborne Simulator, which simulate, respectively, the CALIPSO and MODIS A-train instruments.

To develop a new and modern satellite retrieval method to study the severe storm process, satellite remote sensing is combined with nonlinear chaos dynamics. In this paper, the choice of time delay for the phase space reconstruction for nonlinear time series analyses is carried out. The method based on the information generation is employed. A new algorithm for calculations of the mutual information for the choice of time delay for phase space reconstruction for any probability distribution is developed. To confirm the validity of the algorithm proposed, the tests using simulated time series for some famous chaotic attractors and other nonlinear processes are performed. Finally application of the algorithm in the time series of GMS-5 11μm IR channel brightness temperature observations of rainstorm occurred in Wuhan area in China on 21-27 July 1998 is discussed. The results show that the new algorithm proposed is a good tool for the best choice of time delay in time series.

A quantity called the mutual information dimension is proposed based on the concepts of the information theory and fractal theory. The application of the mutual information dimension in the time series of GMS-5 11μm IR channel brightness temperature observations of the severe rainstorm process occurred in Wuhan area in China on 21-27 July 1998 is carried out. Its application in the simulated time series of the attractor of Henon map is also performed. Furthermore, the key characteristics of the mutual information dimension are discussed. The study indicates that the new quantity is suitable for applications in nonlinear time series analysis.

Two issues relevant to the best choice of time delay for phase space reconstruction are further studied by using the time series of GMS-5 11μm IR channel brightness temperature observations of rainstorm processes occurred in Wuhan area in China in July and in August of 1998. Periodic components existing in the satellite signals are investigated, first. The results demonstrate that the periodic components have noticeable influence on the choice of the optimum time delay. A new algorithm - the derivative method - is then developed for the extraction of possible periodic components from the time series. The advantages of this method and its importance are discussed.

On 29th January 2004 the first Meteosat Second Generation satellite MSG-1, renamed Meteosat-8 (MS-8), commenced routine operations. MS-8 carries the new Spinning Enhanced Visible and Infra Red Imager (SEVIRI) and a Geostationary Earth Radiation Budget (GERB) radiometer. GERB provides valuable short- and long wave broadband measurements of the Earth in order to estimate the top-of-atmosphere radiation budget accurately. The unique feature of GERB in comparison with previous measurements of the Earth's radiation budget is its very fast temporal sampling (15 minutes) afforded by geostationary orbit. On the other hand, the GERB instrument only accounts for a crude spatial resolution (about 50 km at the sub-satellite point). Taking advantage of the synergy between the data from GERB and SEVIRI, we propose at the Royal Meteorological Institute of Belgium to merge the two data streams to produce near real-time estimates of the radiation budget for limited geographical regions at a 3x3 SEVIRI pixel resolution (the SEVIRI resolution is 3 km at satellite sub-point). Such fluxes aim to be used by the climate and numerical weather prediction (NWP) scientific communities through climate studies and validation/evaluation of the performance of NWP models over the region covered by MS-8.

The MODTRAN5(TM) (1a, in press) radiation transport (RT) model is a major advancement over earlier versions of the MODTRAN(TM) atmospheric transmittance and radiance model. New model features include (1) finer spectral resolution via the Spectrally Enhanced Resolution MODTRAN(TM) (SERTRAN) molecular band model, (2) a fully coupled treatment of auxiliary molecular species, and (3) a rapid, high fidelity multiple scattering (MS) option. The finer spectral resolution improves model accuracy especially in the mid- and long-wave infrared atmospheric windows; the auxiliary species option permits the addition of any or all of the suite of HITRAN molecular line species, along with default and user-defined profile specification; and the MS option makes feasible the calculation of Vis-NIR databases that include high-fidelity scattered radiances.

The paper is devoted to the derivation of approximate analytical equations for the top-of-atmosphere reflection function of a cloudy atmosphere. These equations are based on the analytical solution of the radiative transfer equation valid for optically thick clouds. In particular, we consider the radiative transfer both in the gaseous absorption bands and also in the regions, where gaseous absorption can be neglected. The results obtained are of importance for a number of cloud optics problems including cloud optical and microphysical properties determination from spaceborne optical instruments.

In a previous work, an operative procedure to estimate precipitable and liquid water in non-raining conditions over sea was developed and assessed. The procedure is based on a fast non-linear physical inversion scheme and a forward model; it is valid for most of satellite microwave radiometers and it also estimates water effective profiles. This paper presents two improvements of the procedure: first, a refinement to provide modularity of the software components and portability across different computation system architectures; second, the adoption of the CERN MINUIT minimisation package, which addresses the problem of global minimisation but is computationally more demanding. Together with the increased computational performance that allowed to impose stricter requirements on the quality of fit, these refinements improved fitting precision and reliability, and allowed to relax the requirements on the initial guesses for the model parameters. The re-analysis of the same data-set considered in the previous papers showed an improvement of the consistency of the estimates from SSM/I and TMI radiometers and of the agreement with the statistical references. The described work confirmed the stability of the overall approach of the operative Procedure and prepared for new satellite generations (e.g. AMSR-E).

Satellite data measuring aerosols over the Canary Islands need to be correctly interpreted in accordance with the spatial resolution and spectroscopic channels used. In situ data are still a necessary reference for calibrating and interpreting the aerosol index provided by different spectrometers onboard satellites. A comparison of both techniques (in situ and remote) is discussed in this paper, showing there is no linear correlation between the aerosol index and the extinction coefficient. Here, we present an interpretation of different situations arising and discuss critically the correct interpretation of the aerosol index and images provided by the TOMS in accordance with the dust presence over the Observatories. The aerosol index measured at sectors centered at both Observatories (Observatorio del Roque de los Muchachos -ORM-, on La Palma and Observatorio del Teide -OT-, on Tenerife) is also compared.

The Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument, onboard the Meteosat Second Generation (MSG) is a radiometer with 8 infrared (IR) spectral bands. IR retrievals of Layer Precipitable Water (LPW) and Lifted Index (LI) allow to identify potential severe weather when the system is still in a preconvective state. Statistical retrieval is computationally fast and it is a requirement for the SAFNWC PGEs. The study presented here, is part of an attempt to improve the algorithm developed in the SAFNWC framework to calculate Layer Precipitable Water and Stability Analysis Imagery (SAI) from SEVIRI radiances. The first codified algorithms (in the SAFNWC version 0.1 package) are a statistical retrieval where neural networks were trained with the available data (simulated radiances using numerical profiles from 60L-SD and RTTOV-7). These statistical retrievals have been evaluated against co-located products obtained from numerical weather analysis and radiosonde profiles, as well as MODIS products obtained in the areas scanned at the same time. The availability of real SEVIRI radiances allows us to compare real SEVIRI radiances with simulated radiances and to detect systematic bias among both datasets. In this study, first the retrieved LPW and LI will be evaluated, and the error sources will be identified. And later, the method for correcting the detected bias, between real and simulated radiances, will be analysed, and the improvements will be compared to calculated ("clear") values from the nearest (in space and time) ECMWF profiles and similar MODIS products.

The extensive set of measurements performed during the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) experiment provides a unique opportunity to evaluate aerosol retrievals over the ocean from multiangle, multispectral photometric and polarimetric remote sensing observations by the airborne Research Scanning Polarimeter (RSP) instrument. Previous studies have shown the feasibility of retrieving particle size distributions and real refractive indices from such observations for visible wavelengths without prior knowledge of the ocean color. This work evaluates the fidelity of the aerosol retrievals using RSP measurements during the CLAMS experiment against aerosol properties derived from in-situ measurements, sky radiance observations and sunphotometer measurements, and further extends the scope of the RSP retrievals by using a priori information about the ocean color to constrain the aerosol absorption. Satisfying agreement is found for all aerosol products.

The ALOMAR Rayleigh/Mie/Raman (RMR) lidar is an active remote sensing instrument for the investigation of the Arctic middle atmosphere during day and night. It is located in Northern Norway and operated on a routine basis to measure relative density profiles and aerosol properties in the stratosphere and mesosphere since 1995. Temperature profiles derived from the density measurements assuming hydrostatic equilibrium are used to investigate the mean temperature structure as well as gravity waves in the polar middle atmosphere. During the last two years, temperature data were acquired for approximately 2100 hours. A subset of this data basis was used to determine the potential energy density to characterize the gravity wave activity above the station. Noctilucent clouds (NLC) are the highest clouds of the Earth's atmosphere and a visible sign of extreme atmospheric conditions with temperatures far below radiative equilibrium. During the last 7 years a continuous data set with 1880 measurement hours was acquired during the summer seasons, of which 640 hours contain NLC signatures. This actually most extensive lidar acquired NLC archive was analyzed regarding brightness, altitude, vertical extent, as well as occurrence frequency of noctilucent clouds above ALOMAR.

Trace gas distributions and temperatures in the mesosphere and lower thermosphere were derived from infrared spectra measured by the two CRISTA experiments flown in November 1994 and in August 1997. CRISTA (CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere) is a triple telescope cryogenically cooled infrared spectrometer which senses the Earth limb from a Shuttle orbit. The geographical coverage was -57°/+68° and -74°/+74° during the two missions, respectively. Each mission lasted slightly more than one week. The mesospheric set of trace gases include ozone, carbon dioxide and carbon monoxide, methane, water vapor, and atomic oxygen. In addition temperatures and pressures are obtained from the CO2 15 μm band. The temperature/pressure results are used to derive geostrophic wind fields. Most of the data reduction required non-LTE modelling of the radiation properties of the species. Practically all data exhibit considerable large scale structures in both latitude and longitude due to planetary waves or interhemispheric transport.

Gravity waves are ubiquitous in the Earth's atmosphere transporting energy and momentum between regions. GWIM is a satellite instrument that will use airglow intensity variations to measure gravity wave parameters. A major interest lies in the correlation of the presence of gravity waves with their sources near the surface or in the lower atmosphere. The specific airglow emissions were chosen because of their high radiance and their low susceptibility to contamination by moonlight scattered from clouds. GWIM consists of four nadir-looking imagers, one each for signal and background for each of the two emissions. The field of each imager will be 175 km cross-track by 80 km along the track. An integration time of about ten seconds is required to achieve the required signal-to-noise ratio. To prevent image smearing due to the effects of satellite motion and the rotation of the earth, GWIM will operate in snapshot mode with an exposure time of about 0.25 second followed by on-board shift-and-add. GWIM is being considered for flight as part of the payload of EQUARS, a Brazilian satellite planned for launch into a near equatorial orbit in 2007.

Observations of the atomic oxygen green line airglow at 557.7 nm began in England with Lord Rayleigh IV in 1923. The large-scale circulation of the atmosphere is now well known, producing a mesopause that is cold in summer and warm in winter. The corresponding transport of atomic oxygen should produce high airglow emission rates in winter, and low values in summer. Thus remotely sensed airglow observations are potentially capable of providing a record of the large-scale circulation of the thermosphere. Here a search is made for the signature of the large-scale circulation using data from the WIND Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite, and model results from the TIME-GCM model, making use of earlier ground-based results as well. However, the signature of this circulation is not readily found. In the tropical region a well-defined semi-annual variation of emission rate is identified; this appears to result from the semi-annual variation of the diurnal tide. At mid- and high latitudes a pronounced annual variation is found with an emission rate maximum in the autumn in both hemispheres. At still higher latitudes ground-based observations show this strong autumn maximum, with deep depletion of atomic oxygen in the springtime.

The SABER radiometer on the TIMED spacecraft scans the earthlimb continuously in ten channels spanning the spectrum from 1.27 to 15 μm. The signature of the diurnal tide in the equatorial region is apparent throughout the mesosphere in TIMED/SABER data, especially in the CO₂ 15-μm radiance profiles. In addition, layer structures are apparent in a large fraction of the both the radiance profiles and the kinetic temperature profiles derived from them. We present results showing tidal and layer features in the variation with local time and latitude of 15-μm radiance and temperature. Temperature inversion layers (TILs) are regions of extreme perturbations in the retrieved temperature profile where the temperature increases rapidly over 3-10 km range by tens of degrees K, sometimes approaching increases of 100 K, and are not represented in any existing atmospheric climatologies. Theories that have been proposed connect them with the amplitude and phase of atmospheric tides, as well as with the interactions and dissipation of atmospheric gravity waves and planetary waves. The radiance local maxima, or "knees," are more mysterious. Their occurrence is rather unpredictable and not well explained by models, although it is known that they are due to vibrational excitation of CO₂ by atomic oxygen and they may have tidal connections. While they may be associated with strong TILs, the most important class occurring at tangent heights in the lower thermosphere between 100 and 115 km appear not to be simply related to local inversion layers. SABER data offers the opportunity to do the first global survey of MLT TILs, determine their spatial extent and persistence time, and develop a global climatology of their occurrence and properties.

A retrieval processor based on rapid forward modeling algorithms and an optimal estimation approach has been developed at Forschungszentrum Juelich, Germany. It has been used to derive global distributions of the chlorofluorocarbons CFC-11 and CFC-12 from Envisat MIPAS measurements. We give a detailed description of the retrieval system, show error analyses, and discuss briefly the seasonal behavior of CFC-11 and CFC-12 for January to March and July to September 2003.

The ability of SAGE III to retrieve ozone, NO₂ and aerosol vertical distribution within Earth atmosphere from limb scatter measurements is being investigated. The sunlight scattered by atmospheric gases and particulates (aerosol, clouds) and the Earth's surface is measured and spectrally dispersed by SAGE III spectrometer. Ozone density vertical profiles are retrieved from 10 km (or cloud top) to 50 km at a resolution of about 1 km and a precision of less than 10 % using Chappuis and Huggins ozone absorption bands. NO₂ vertical density profiles are retrieved from 15 to 40 km at a resolution of about 2 km and a precision of 20% using the NO₂ absorption features in the 430-450 nm spectral range. Aerosol extinction vertical profiles (from 15 to 30 km) are retrieved using a series of non absorbing channels. Retrieved products are compared with available correlative data (ozone sondes, SAGE III in occultation, OSIRIS).

Atmospheric Motion Vectors (AMVs) are one of the most important products generally derived from all geostationary satellites, and especially from Meteosat at EUMETSAT, because they constitute a very important part of the observation data fed to Numerical Weather Prediction. The resolution of the current operational products is 160 km at the sub-satellite point. The height assignment is currently the most challenging task in the AMV extraction scheme. The main approach used for Meteosat was the so-called 'WV-IRW intercept method' for semi-transparent cases. Opaque cloud heights are calculated from the representative Equivalent Black Body Temperatures derived from the AMV target area. The advent of Meteosat 8 provides many new opportunities for improve height assignment of AMVs. Existence of a CO2 absorption channel at 13.4 μm on SEVIRI instrument enables to use simultaneously the IR/CO2 ratioing methodology in addition to the semi-transparency technique. Due to the existence of several Water Vapour and Infrared channels on SEVIRI, each method can be implemented in slightly different configuration, and finally, there are 15 cloud top pressure schemes implemented in the MSG-MPEF. This paper presents a comparison of some of these methods using Meteosat 8 data.

A new differential measurement concept is presented for retrieving the total content of water vapor (IWV, Integrated Water Vapor) along the propagation path between two Low Earth Orbiting (LEO) satellites, while such path is immersing in the atmosphere during a so called set occultation. The new approach, referred to as DSA (Differential Spectral Absorption) method, is based on the simultaneous measurement of the total attenuation at two relatively close frequencies in the K band, and on the estimate of a "spectral sensitivity parameter" that is highly correlated to the IWV content of the LEO-LEO link in the low troposphere. The DSA approach has the potential to overcome all spectrally 'flat' and spectrally correlated phenomena (atmospheric scintillation among these) and provides estimates that can then be usefully integrated with standard radio occultation data products. In the paper we describe the signaling structure chosen for DSA measurements and the transmit-receive system used to simulate an end-to-end transmission during a complete LEO-LEO set occultation. Simulations are based on atmospheric models and on real radiosonde data, which allows us to account for the natural variability of the atmospheric conditions. The effects on the IWV estimates of impairments such as thermal noise at the receiver, atmospheric scintillation, multipath and defocusing are evaluated.

A substantial upgrade of our previously developed MFRSR data analysis algorithm is presented. The new version of the algorithm features an automated cloud screening procedure based on optical thickness variability analysis. This technique is objective, computationally efficient and is able to detect short clear-sky intervals under broken cloud conditions. The performance of the method has been compared with that of AERONET cloud screening algorithm. Another new feature is the adoption of a bimodal gamma distribution as the aerosol particle size model. The size of the fine mode particles and a ratio between optical thicknesses of the two modes are retrievable. The algorithm has been tested on a multi-year dataset from the MFRSR network at the DOE Atmospheric Radiation Measurement (ARM) Program site in Southern Great Plains (SGP). The aerosol optical thicknesses (total, fine, and coarse) obtained from our analysis were successfully compared with the corresponding AERONET almucantar retrievals from a CIMEL sunphotometer colocated with the MFRSR at the SGP Central Facility. Geographical and seasonal variability of aerosol properties has been observed in the multi-instrument dataset from all SGP Extended Facilities for the year 2000. The geographical trends in the fine mode particle size appear to reflect differences in the PM2.5 to PM10 ratios obtained from EPA monitoring data. Long-term temporal variability has been studied on the 1992-1997 dataset from the SGP Central Facility. A significant trend has been detected in coarse mode aerosol optical thickness following the Mt. Pinatubo eruption in 1991, while the fine mode optical thickness exhibits only seasonal variations during that period.

The Vaisala ceilometer LD40 is an eye-safe commercial lidar. It is designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. The instrument was operated continuously at different measurement campaigns to detect mixing layer height from aerosol backscatter profiles. First results with the CT25K ceilometer were presented last year in the paper SPIE 5235-64 from the environmental measuring campaign in the frame of the BMBF-funded project VALIUM in Hanover, Germany, investigating the air pollution in a street canyon and the surrounding with various sensors. A software for routine retrieval of mixing layer height (MLH) from ceilometer data was developed. A comparison with mixing layer height retrievals from a SODAR and a wind-temperature-radar (WTR) operated in the urban region of Munich will be shown. The three instruments give information that partly agree and partly complement each other. The ceilometer gives information on the aerosol content of the air and the WTR provides a direct measurement of the vertical temperature distribution in the boundary layer. The WTR and the ceilometer add information on the moisture structure of the boundary layer that is not detected by the SODAR which gives information on the thermal structure. On the other hand this comparison validates known techniques by which the MLH is derived from SODAR data. In the absence of low clouds and precipitation ceilometers can estimate the mixing-layer-height fairly well. The potential of the ceilometer, being the smallest instrument among the used ones as LIDAR, SODAR and WTR, will be discussed to be used in future MLH studies.

We present an analysis of the aerosol retrieval capabilities of different types of satellite measurements. Here, we consider single- and multiple-viewing-angle measurements of intensity and of intensity together with polarization. In particular, we investigated their information content with respect to aerosol size distribution, optical thickness, and refractive index. For our investigation we employed a newly developed linearized vector radiative transfer model. This radiative transfer model accurately simulates the intensity vector and additionally calculates the derivatives with respect to the relevant aerosol properties. The use of an accurate linearized radiative transfer model in combination with an analytical inversion approach allows a solid error analysis and quantification of the information content of the different measurement types. In order to obtain optimal aerosol information from satellite measurements, multiple-wavelength multiple-viewing-angle measurements of intensity and polarization are needed. Furthermore, multiple-wavelength multiple-viewing-angle measurements of only intensity provide better aerosol information than multiple-wavelength measurements of intensity and polarization in one viewing direction. On the other hand, for single-viewing-angle instruments the inclusion of polarization leads to an improvement in accuracy in effective radius, refractive index, and optical thickness of a factor 10-100 compared to intensity measurements alone. Here, the inclusion of polarization has an even stronger effect than for multiple-viewing-angle measurements.

Aerosol optical properties are retrieved from measurements acquired during the 2003 summer at the new AERONET station of Evora, Portugal, with a sun/sky photometer, a fluxmeter and a nephelometer. Aerosol optical thickness (aot) derived at several wavelengths shows that an exceptionally long turbid event occurred in July-August. Desert dust particles transported from North Africa increased aot at 873 nm (aot873) to the value of 0.27 with an Ångstrom exponent α_C=0.5. Emissions from forest fires in The Iberic peninsula affected Evora since the end of the dust episode, with aot441 reaching 0.81 and aC=1.8. The aerosol scattering coefficient measured at surface level shows that desert dust does not reach the surface level at Evora while the forest fire emissions were uniformly distributed over the atmospheric column. Sky-radiance and flux measurements agree in retrieval of the aerosol single scattering albedo (assa) at several wavelengths. A large absorption rate is found with a high spectral dependence for desert dust particles (assa441=0.86 and ass873=0.93) and with a flat spectral dependence during the forest fires emission episode (assa441=0.88 and assa873=0.87). All measurements as well as back-trajectory calculations indicate mixture of particles during the desert dust.

Our recent work has demonstrated the feasibility of using satellite-derived data to draw quantitative maps of particulate loading within the planetary boundary layer. Our method, when used in conjunction with atmospheric dispersion models and ground data, can provide a comprehensive estimate of tropospheric pollution from particulate matter. Information filtering techniques are used to reduce the error of the information fusion algorithm and, consequently, produce the best possible estimate of tropospheric aerosol. Two data filtering methods have been used and their effectiveness with regard to overall error reduction is determined in this work. The first one is based on a weight scheme to take into account an empirical estimate of local error and/or uncertainty in input data. The second uses a modified Kalman filter for error reduction. The effectiveness of each of the filtering techniques depends on factors such as relative error variance across the computational domain, and precision of model input, i.e. on the accuracy of the ground emissions inventory and the reliability of measured ambient aerosol concentrations. The ICAROS NET fusion method was applied in the greater area of Athens, Greece over several days of observation in order to assess conclusively the adequacy of the information fusion filters employed.

The Improved Limb Atmospheric Spectrometer-II (ILAS-II) onboard the Advanced Earth Observing Satellite-II (ADEOS-II) was successfully launched on 14 December, 2002 from Japan Aerospace Exploration Agency (JAXA)'s Tanegashima Space Center. ILAS-II is a solar-occultation atmospheric sensor which measures vertical profiles of O₃, HNO₃, NO₂, N₂O, CH₄, H₂O, ClONO₂, aerosol extinction coefficients etc. with four grating spectrometers. After the checkout period of the ILAS-II, ILAS-II started its routine operation since 2 April 2003 until 24 October 2003, when ADEOS-II lost its function due to solar-paddle failure. However, about 7 months of data were acquired by ILAS-II including whole period of Antarctic ozone hole in 2003 when ozone depletion was one of the largest up to now. ILAS-II successfully measured vertical profiles of ozone, nitric acid, nitrous oxide, and aerosol extinction coefficients due to Polar Stratospheric Clouds (PSCs) during this ozone hole period. The ILAS-II data with the latest data retrieval algorithm of Version 1.4 shows fairly good agreement with correlative ozonesonde measurements within 15% accuracy.

The air quality in Munich is monitored by the measurement network of the Bavarian Agency for Environmental Protection. Additional information can be provided from retrievals of optical thickness and corresponding particle concentrations from satellite images in an area of approximately 100 km x 100 km (depending on the satellite sensor used). The satellite measures the optical thickness of the entire atmosphere, which has to be attributed mainly to the mixing layer. The mixing layer height is determined either by remote sensing, by radiosondes, or by numerical models of the boundary layer. The corrected optical thickness of the satellite images can be interpreted as the particle concentration in the mixing layer. Data from the ground-based monitoring network and from satellite retrievals are fused in the ICAROS NET platform. This platform is applied to supply additional information on the air quality in the Munich region and it is tested as well as evaluated during field campaigns in summer and winter. The adaptation to the Munich region covers the development of routines for the collection of data, for example from the measuring network, and the disposal of information, which were defined by the Bavarian agency for environmental protection. During measurement campaigns in and around Munich PM 10, PM 2.5 and PM 1.0 concentrations and mixing layer heights by remote sensing (SODAR, ceilometer, WTR) were determined. Temporal variations of the concentration, the spatial distribution (3 measurement locations) and concentration conditions for selected particle sizes are presented.

Atmospheric concentration measurement of nitrogen dioxide (NO₂) pollutant was demonstrated by a new type of differential optical absorption spectroscopy (DOAS) using a spectral scanning device of a visible acousto-optic tunable filter. The measurement requires a stable artificial light source such as a xenon lamp, and the light beam is directed into the environment where the concentration of NO₂ is to be monitored. The retrieval of NO₂ concentration is then achieved by analyzing the residual light using the DOAS signal processing. In this paper, we present results obtained from this new DOAS system during continuous measurement of atmospheric NO₂ concentration in the campus of the City University of Hong Kong. Another DOAS system, using a miniature CCD grating spectrometer, was established as a control experiment. The CCD spectrometer acts as a traditional DOAS system for performance evaluation. Instead of using the NO₂ absorption cross section for concentration retrieval, differential absorption area provides an alternative quantity for concentration retrieval. The monitoring results from both of the DOAS systems are compared with the pollutant concentrations reported in a nearby pollutant monitoring station, operated by the Hong Kong Environmental Protection Department.

Widespread boreal forest fires persisted in Eastern Asia for several months from the beginning of April until September 2003. This resulted in enhanced concentrations of smoke aerosol in a very large region, ranging from the source area of the fires in eastern Siberia to northern and eastern China, Korea, and Japan. The smoke was also detected over large areas of the Pacific Ocean, and was even observed in Alaska. E.g., during mid-May aerosol optical thickness values higher than 4 at mid-visible wavelengths were observed on the ground at Anmyon, Korea, due to transport of forest fire aerosol to this region. Satellite remote sensing provides a very useful tool to observe the temporal evolution and the spatial distribution of the aerosol over large areas. In this work, we employ a newly developed algorithm for the ADEOS-2/GLI sensor, that was launched onboard the ADEOS-2 sensor in December 2002. The algorithm employs two channels in the near-UV to retrieve the aerosol optical thickness and single-scattering albedo of aerosols. Although GLI had only a 7-month lifetime due to the early power failure of the ADEOS-2 satellite in October 2003, it was able to observe the whole period of large-scale forest fire smoke, that heavily impacted Eastern Asia. We also analyze ground based skyradiometer measurements at Sapporo, Japan, which was frequently influenced by forest fire aerosols during spring 2003.

Information about the interaction between the exhaust plume of an aircraft jet engine and ambient air is required for the application of small-scale chemistry-transport models to investigate airport air quality. This interaction is not well understood. In order to study the interaction, spatial information about the plume is required. FTIR emission spectroscopy may be applied to analyze the aircraft exhausts. In order to characterize the plumes spatially, a scanning imaging FTIR system (SIGIS) has been improved. SIGIS is comprised of an interferometer (Bruker OPAG), an azimuth-elevation-scanning mirror, a data acquisition and control system with digital signal processors (DSP), an infrared camera and a personal computer. With this instrumentation it is possible to visualise the plume and to obtain information about the temperature distribution within the plume. Measurements are performed at low spectral resolution, because the dynamic environment of these measurements limits the measurement time to about 2 minutes. Measurements of the plume shapes of an APU and of main engines were performed.

The sensitivity of commercial lidar ceilometers for detecting aerosols within the boundary layer is sufficient to give reliable information on parameters like the mixing layer height. The traditional optical concepts of these lidars are either biaxial two-lens systems or one-lens systems with separate compensation techniques for the internal optical cross talk. The single lens concept is superior to the biaxial system when reliable data from the near range up to 300 m elevation is required. This paper introduces an enhanced single lens system removing the internal optical cross-talk between the laser transmitter and the receiver. The new Vaisala Ceilometer CL31 uses this optical layout to improve cloud and vertical visibility detection performance in precipitation, fog and haze situations. On the other hand it also provides advanced boundary layer scans during clear sky weather. Such scans are performed around the clock in the Vaisala test field by ceilometers using the three optical systems discussed. A comparison of cases covering a variety of different meteorological situations illustrates the advantages of the new optical concept. Mixing layer height values are determined with a gradient method and compared to radio sounding data.

A method based on the advantage of a bi-wavelength lidar system has been developed and tested. The method departs from the fact that in nearly transparent atmospheres (weak extinctions), the ratio of the lidar signals at both wavelengths gives the Ångstrom exponent in backscatter with very low uncertainty. The method consists in (i) assuming a linear relationship between the Ångstrom exponent in backscatter and the Ångstrom exponent in extinction (usually called Ångstrom exponent), (ii) approximating by a first order development the ratio of the transmittances, (iii) and forcing the resulting Ångstrom exponent. Profiles of the Ångstrom exponent, and the aerosol backscatter coefficient at 1064 and 532 nm were retrieved. The aerosol backscatter coefficient profiles were compared to Klett inversion results in the lowest part of the atmosphere containing aerosols, [0 - 3 km], in a rural environment in summertime: the agreement is better than 12 % at 1064 nm, and better than 35 % at 532 nm, indicating a greater dependency to the initial assumptions in the visible range.

The ability to accurately validate high spectral resolution infrared radiance measurements from space using comparisons with aircraft spectrometer observations has been successfully demonstrated. The demonstration is based on an under-flight of the Atmospheric Infrared Sounder (AIRS) on the NASA Aqua spacecraft by the Scanning High resolution Interferometer Sounder (S-HIS) on the NASA ER-2 high altitude aircraft on 21 November 2002 and resulted in brightness temperature differences approaching 0.1K for most of the spectrum. This paper presents the details of this AIRS/S-HIS validation case and also presents comparisons of Aqua AIRS and Moderate Resolution Imaging Spectroradiometer (MODIS) radiance observations. Aircraft comparisons of this type provide a mechanism for periodically testing the absolute calibration of spacecraft instruments with instrumentation for which the calibration can be carefully maintained on the ground. This capability is especially valuable for assuring the long-term consistency and accuracy of climate observations. It is expected that aircraft flights of the S-HIS and its close cousin the National Polar Orbiting Environmental Satellite System (NPOESS) Atmospheric Sounder Testbed (NAST) will be used to check the long-term stability of the NASA EOS spacecrafts (Terra, Aqua and Aura) and the follow-on complement of operational instruments, including the Cross-track Infrared Sounder (CrIS).

The particles of upper clouds are ice crystals with various sizes and shapes. Under certain conditions they can be oriented in space. This circumstance leads to the significant anisotropy of light in cirrus clouds that should be taken into account when solving problems of radiation propagation through the atmosphere. Acquiring the information on parameters of particle orientation in ensembles of actual clouds is still an urgent and poorly studied problem. In this connection, we have developed a lidar technique for measuring the backscattering phase matrices (BSPM) that enables one to acquire such information. Based on processing of 450 experimentally measured BSPMs we have drawn the following conclusions: - in 90 to 95 % cases the orientation of the larger diameters of particles along the azimuth direction was observed, though in 70% of these cases the orientation was only weakly pronounced against the background of particles that had no preferred orientation in the azimuth plane. However, the backscattering coefficients for linearly polarized light can strongly depend on the orientation of the polarization plane. - the larger diameters of particles practically always lied in the horizontal plane, and in 50% cases the degree of this orientation should be recognized essential. The latter means that the extinction coefficient of such clouds should strongly depend on the angle of radiation incidence on the cloud layer.

Cloud cover constitutes a major challenge for the surface albedo estimation using AVHRR data. The demand of pixelwise high accuracy cloud masking based on only single AVHRR images without any augmenting information is not realistic in all possible conditions of cloud fraction and cloud type on any land cover type. Another approach to tackle cloudy conditions is presented in this study. In the areas studied (Finland, Switzerland, the Netherlands) cloudy broadband albedo distributions were constructed for AVHRR data of one month and 15 km x 15 km area. The peak of the distribution, which is caused by the clear sky conditions, correlated well with the corresponding surface albedo distribution obtained from pyranometer measurements at Sodankylä, Payerne and Cabauw masts. Using the half and ¾ height points of the peak it was possible to estimate the surface albedo with quite good accuracy using a simple physically motivated formula.

The Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging Spectroradiometer (MISR) are two of the instruments aboard the Terra Earth Observing System (EOS). Algorithms for the retrieval of cloud-top heights have been implemented in order to get a product that can be applied in climate change studies, climate modeling and atmospheric research. Cloud height information can be used to analyze the Caribbean climate and to understand deforestation patterns on rain forests. The algorithms to retrieve this kind of information are based on CO2 slicing method and stereo matching methods. Cloud height information appears in terms of cloud top pressures. To compare MODIS cloud top pressures with MISR cloud top heights, it is important to look for a good atmospheric profile for the Caribbean such as by looking at field instrument observations. Available data from MODIS and MISR is geolocated in different latitudes and longitudes. MISR technique is an innovative method that assigns height values in a geometric form. In order to compare MODIS cloud-top pressures and MISR cloud-top heights, cloud-top pressures must be converted into cloud-top heights. Upper air observations can be used to get pressure-height profiles over the Caribbean. Also this kind of data can be used to validate MODIS and MISR parameters. Do cloud height measurements from MODIS can be better comparing to MISR measurements? Do cloud height measurements from MODIS or MISR can be used to classify cloud types? How confident are the conversion methods in order to compare these two sensors?

At the beginning of an air pollution event, pollutants are emitted into the atmosphere by a variety of sources. The knowledge of the emissions of every source is inevitable to carry out adequate reduction measures. Sometimes, the estimation of source strengths from afar is necessary due to the lack of accessibility to the source (e.g.: aircraft in use) or due to the diffuse character of the source (e.g. area sources). Source strengths and concentration measurements are connected by the transport of the pollutant, which can be estimated using a dispersion model. The underlying idea to determine the source strength is to run the dispersion model varying the input parameters as long as needed to obtain the least possible difference of measured and modelled concentrations. The model input is then assumed to be the best estimation of the emission rates. Assuming a passive pollutant, the transport and dispersion can be condensed into a set of linear equations and hence, linear algebra can be used to solve for the source strength (e.g. Singular Value Decomposition). The advantage of concentration measurements along a horizontal path (e.g. by FTIR, DOAS) is to reduce the degree of uncertainty regarding the horizontal dispersion. So the main interest of the modelling approach is to estimate the amount of vertical dispersion that accounts for the dilution of the pollutants. Applying this method to a real case with highly heterogeneous source characteristics in time and space, measurements at an international airport were performed. Some results of these measurements are presented here.

We report on the progress of a far-infrared/submillimeter radiometer being developed in Cardiff for the measurement of cirrus clouds. Remote sensing of cirrus clouds is known to be of great importance to the long-term accuracy of current General Circulation Models (GCM) and climate prediction but with greater measurement coverage needed. The instrument reported here is an aircraft deployed, 5 channel fixed band radiometer capable of retrieving cirrus Ice Water Path (IWP) and mean particle diameter (D_me) using a spectral range of between 10 cm^-1 and 55 cm^-1. The radiometer will capitalise on ongoing measurements from the Fourier transform interferometer based, Far-infrared Sensor for Cirrus (FIRSC), an instrument for which Cardiff has been closely associated. Initial results of channel selection simulations are presented here with comparisons between different combinations of channel frequency and bandwidths, along with the number of channels used and cloud particle shape. Also demonstrated is the effect of instrument noise on retrieval performance which is shown to be the dominant source of retrieval error.

For years the use of satellite data has increased in the assimilation systems for numerical weather prediction models. Data from nadir viewing passive microwave sounders has mainly been used in the global assimilation systems. The use has also been increased to regional models, mainly due to the improved information extraction possible with varational assimilation schemes and the improved possibilities of near real time data access. We describe the system implemented at the Danish Meteorological Institute for assimilating ATOVS AMSU-A data. Initially over open water and cloud free area due to the relative simple surface charactersitics. Currently the system is under development to include data usage over land and sea-ice. For this purpose we only use data from a reduced number of channels. The original open water assimilation gave slight positive impact in the winter season and positive or neutral impact during summer season. The extended data usage over sea ice will increase the amount of used data significantly, and is expected to give further positive impact, most noticeable at high latitudes.

A general methodology for rating both performance and potential of lidar systems used for detection of atmospheric trace constituents is developed. This is carried out via a generalized figure of merit, V, for lidar quality by consideration of both lidar system parameters and atmospheric operating conditions on signal-to-noise-ratio. Based on V and atmospheric parameters, computer simulations are carried out and simple design procedures are outlined to determine achievable lidar performance and ensure the best monitoring efficiency for a given set of initial requirements.

Fourier Transform Infrared (FTIR) spectroscopy is a well-established technique for monitoring air pollutants by extractive methods. Remote sensing by Open-Path FTIR technique incorporates the advantages of a non-intrusive technique. EPA and VDI have recommended some guidelines for the application of this promising technique. However, it is necessary to do more research to assess the quality of these systems on the basis of European standards. The analysis of FTIR spectra are usually carried out by using methods based on classical least squares (CLS) procedures. In this work a line-by-line method (SFIT) is additionally used. SFIT is a non-linear least-squares fitting program that was designed to analyse solar absorption spectra. For this work, SFIT has been adapted and applied to Open-Path FTIR spectra. The objective of this work is to study the capability of both methods to analyse open-path measurements of carbon monoxide. From a previous work it was inferred that the selection of the analysis spectral window is a relevant parameter of SFIT analysis. Therefore, the first step has been to analyse synthetic spectra of known concentration to select the best spectral region and other parameters of analysis. Afterwards, the SFIT software has been applied to Open-Path experimental spectra. Results of the SFIT method have been compared with the results of the two methods of EVAL analysis. EVAL is a commercial software (provided with the instrument) that is based on a CLS procedure and on the absorption peak intensity. The result has been validated by comparison to a standard extractive method.

An open-path Fourier Transform Infrared (FTIR) and a Differential Optical Absorption Spectrometer (DOAS) were installed and simultaneously operated along a 426 m optical path in downtown Mexico City. O₃ and SO₂ were measured by both optical remote sensing techniques and the results from the comparison are presented. The instruments presented comparable sensitivities for O3 and an excellent agreement (R2 > 0.99) in their correlation. Although the sensitivity of the infrared technique for SO₂ was limited to concentrations > 20 ppb or so, the agreement of the FTIR response with the more sensitive DOAS technique during the high levels of this pollutant was favorable (R2 = 0.94) and accurate to within experimental error. These episodes (>100 ppb) were found to occur several times per month. Benzene and toluene were measured by the DOAS technique and their concentrations are reported for a 3-month period during 11/2 - 12/5, 2003. The mean and highest concentration registered for benzene was 5.1 and 18.7 ppb, respectively, with an average of daily maxima at 11.5 ppb. Toluene's highest concentration during this period reached 97.3 ppb, with a mean and daily maximum average of 13.4 and 41.7 ppb, respectively. A benzene/toluene ratio of 2.6 was determined for the entire period of study and a decrease of ~20% in the daily ambient concentration of these aromatic hydrocarbons was observed on Sundays relative to weekdays.